Question

In a polypeptide chain of 125 amino acids, if the 25th amino acid is mutated to the UAA then
(a)A polypeptide of 124 amino acids is formed.
(b)A polypeptide of 25 amino acids is formed.
(c)A polypeptide of 24 amino acids is formed.
(d)Any of the above can be possible.

Answer 1

Since UAA is the end codon in any polypeptide chain so, once it appears on the chain further coding of amino acids will be stopped. The mutation is a change in the sequence of DNA. It occurs due to autoimmune disease or infectious diseases. It may also occur due to exposure to ionizing radiation.

Complete answer:
If the 25th amino acid gets mutated to the UAA in a polypeptide chain of 125 amino acids then a polypeptide of 24 amino acids is formed because UAA is an end codon it does not code for any amino acids.

Additional Information: -As we know amino acids are associated with protein synthesis and protein synthesis is a process by which proteins are made by cells.
-The synthesis of proteins occurs in two steps transcription and translation.
-Transcription is a process in which DNA is converted to transfer RNA by the help of enzyme RNA polymerase and the process involved is named transcription.
-The process of conversion of transfer RNA into the amino acid chain is known as translation.
-It occurs by the initiation of a polypeptide chain and AUG ie. methionine is the initiation codon or it can also be known as a start codon. From this, the amino acid chain continues till it reaches the stop codon that means UAA, UAG, and UGA.
-Once the stop codon is received further protein synthesis stops the protein is translocated to the target site.
-The stop codons are also known as nonsense codons as they do not code for any amino acids.
-Hence if the 25th amino acid is mutated by the end codon the protein synthesis is terminated and a polypeptide chain of 24 amino acids is formed.
-The polypeptide chain of 125 amino acids is formed only when the 126th codon works as an end codon.
So, the correct answer is, 'A polypeptide of 24 amino acids is formed'.

Note: -The stop codon for the and codon terminates the further translation of protein.
-UAA, UAG, and UGA are called nonsense codons because they do not code for any amino acids.
-For the growth development and proper functioning of the body protein synthesis is very much necessary.